Update doorkeeper requirement from >= 5.5, < 5.7 to >= 5.5, < 5.8

Updates the requirements on [doorkeeper](https://github.com/doorkeeper-gem/doorkeeper) to permit the latest version.
- [Release notes](https://github.com/doorkeeper-gem/doorkeeper/releases)
- [Changelog](https://github.com/doorkeeper-gem/doorkeeper/blob/main/CHANGELOG.md)
- [Commits](doorkeeper-gem/doorkeeper@v5.5.0...v5.7.0)

---
updated-dependencies:
- dependency-name: doorkeeper
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

doorkeeper-openid_connect.gemspec

@@ -24,7 +24,7 @@ Gem::Specification.new do |spec|
 
   spec.required_ruby_version = '>= 2.7'
 
-  spec.add_runtime_dependency 'doorkeeper', '>= 5.5', '< 5.7'
+  spec.add_runtime_dependency 'doorkeeper', '>= 5.5', '< 5.8'
   spec.add_runtime_dependency 'jwt', '>= 2.5'
 
   spec.add_development_dependency 'conventional-changelog', '~> 1.2'